There is Japanese Patent Laid-Open No. 2014-23142 (PTL 1) as a background art of this technical field. In this publication, there is the following description: “There is provided a cloud computing subsystem for computing resource provisioning having various service levels on a specific network separation area. Further, there is provided a protocol for controlling flows of frames from tenants in the cloud computing subsystem and to the tenants.” (see the abstract).